Electrically focussed laser diode

ABSTRACT

A laser diode for producing focused or defined divergent light comprises a semiconductor crystal having a planar PN junction and two parallel end faces extending perpendicular to the PN junction and conjointly forming a resonator for optical radiation. The end faces comprise portions of two confocal surfaces. The PN junction extends between the two confocal surfaces in a radial plane relative to the focal locus. One of the end faces is impermeable to optical radiation and the other of the end faces is a mirror partially permeable to optical radiation.

United States Patent Heinz Henker Munich. Germany [72] Inventor 1211Appl. Mov 860,634 [22] Filed Sept. 24. 1969 145] Patented July 13.1971[73] Assignee Siemens Alttiengesellschaft Berlin, Germany 1321 PrioritySept. 30. 1968 [33] Germany [31] Pl78906l.8

1541 ELECTRICALLY FOCUSSED LASER DIODE 8 Chlms,4 Drawing Figs.

{52} US. Cl. 331/945. 317/234, 356/120 3 6/210 [51]1nt.Cl......,,...,..,... H v H01s3/l8 [S0] FieldofSearch 331/945;

317/234; ass/1263101537, 209. 210

[56] References Cited UNITED STATES PATENTS 2,311,101 2/1943 Tuttle356/210 2,730,922 H1956 Beard 356/210 2.806.401 9/1957 Demuth et a1.356/237 3245002 4/1966 Hall 391/945 10 4 3 2/196 Garflnkel et al 391/9453.344.365 9/1967 Lewis 391/945 3,395,368 7/1968 Koester 391/9453,402,366 9/1968 Williams et a1 391/9415 3,451,008 6/1969 Dunne 391/9453,517,281 6/1970 Mlovsky etal. 317/237 3.531028 10/1970 Pankove 331/945FOREIGN PATENTS 640,691 7/1960 Great Britain Primary Examiner-R. L.Wibert Assistant Examiner Edward S. Bauer At!0rneys-Curt M. Avery,Arthur E. Wilfond, Herbert L.

Lerner and Daniel .1. Tick ABSTRACT: A laser diode for producing focusedor defined divergent light comprises a semiconductor crystal having aplanar PN junction and two parallel end faces extending perpendicular tothe PN junction and conjointly forming a resonator for opticalradiation. The end faces comprise portions of two confocal surfaces. ThePN junction extends between the two confocal surfaces in a radial planerelative to the focal locus. One of the end faces is impermeable tooptical radiation and the other of the end faces is a mirror partiallypermeable to optical radiation.

ATENTEU JUN 3191.

ELECTRICALLY FOCUSSED LASER DIODE DESCRIPTION OF THE INVENTION Theinvention relates to a laser diode. More'particularly, the inventionrelates to an electrically focused laser diode.

The diode of my invention produces focused or defined divergent light.The laser diode comprises a semiconductor crystal having a planar PNjunction and two parallel end faces extending perpendicularly to said PNjunction and forming a resonator for optical radiation.

The laser diodes or luminescence diodes function in accordance with thelaser principle. A'B' semiconductor crystal, particularly galliumarsenide, with two oppositely doped areas or regions, as known.

A laser diode is basically a semiconductor diode, defined by at leasttwo exactly planar-parallel end faces extending perpendicularly to thePN junction, in the form ofa resonator in accordance with the principleof the Fabry-Perot interferometer and operated in the forward directionThe radiation emittable energy states are excited electrically ratherthan by optical means as in other solid state laser types. Theelectrical excitation of the radiation-emittable energy states iseffected in a laser diode by the injection of electrons and holes intothe barrier layer or PN junction of the diode and in a very narrowregion adjacent both sides of the PN junction area. The wavelength ofthe emitted radiation is determined in a semiconductor primarily by thewidth of the forbidden zone of the semiconductor material utilized.

Until my invention, it has been customary to utilize suitable opticalauxiliary means such as, for example, lenses and mirror devices, forfocusing or producing a defined divergent bundle or beam of coherentlight, produced in the laser diode. The utilization of optical auxiliarydevices of this type is relatively intricate, necessitating an exactadjustment of the individual components. Furthermore, the intensity ofthe produced light is diminished by absorption.

The principal object ofthe present invention is to provide a new andimproved laser diode.

An object of the invention is to focused laser diode.

An object of the invention is to provide a laser diode which produces adefined divergent bundle of light or a very intensive, narrow strip orpoint of light, having a diameter or width ofa few microns.

An object of the invention is to provide a laser diode which producesfocused or defined divergent light with a simple structure, efficiency,effectiveness and reliability.

in accordance with my invention, a laser diode for producing focused ordefined divergent light comprises a semicon ductor crystal having aplanar PN junction and two parallel end faces extending perpendicular tothe PN junction and conjointly forming a resonator for opticalradiation. The end faces comprise portions of two confocal surfaces. ThePN junction extends between the two confocal surfaces in a radial planerelative to the focal locus. One of the end faces is impermeable tooptical radiation and the other of the end faces is a mirror partiallypermeable to optical radiation.

Each of the confocal surface portions may be of spherical configurationand the plane of the PN junction extends through the center of thesphere. Each of the confocal surface portions may be of cylindricalconfiguration and the plane of the PN junction extends perpendicularlyto the axis of the cylinder.

The one of the end faces at the greater radial distance from the focallocus may be impermeable and the other of the end permeable to opticalradiation. The one of the end faces at the shorter radial distance fromthe focal locus may be impermeable and the other of the end faces may bepartially permeable to optical radiation.

The semiconductor crystal has two contact faces on opposite sides ofthecrystal extending parallel to the plane of the PN junction. Electricalcontact and heat sink structures may provide an electrically ffitrs mayhe partially A laser diode comprises an be in conductive contact withthe contact faces of the semiconductor crystal. Each of a pair ofelectrical contact blocks of good heat conducting material may be inconductive contact with a corresponding one of the contact faces of thesemiconductor crystal.

Each ofa pair oflight-rcsponsive sensors may be affixed to acorresponding one of the sides of the crystal. Each of the sensorsextends away from the semiconductor crystal substantiallyperpendicularly to the corresponding sidev Each of the light-responsivesensors is of area-type and has a length which is greater than thegreatest distance between the contact faces ofthe semiconductor crystal.

The semiconductor crystal has a dimension perpendicular to the PNjunction which does not substantially exceed the luminescent regionofthe semiconductor crystal.

It is thus seen that, in accordance with my invention, the end faces ofalaser diode are designed as portions oftwo confocal spherical orcylindrical surfaces, wherebetween the surface of the PN junctionextends in radial directions. One of the end faces is impermeable tooptical radiation and the other of the end faces is partially permeableto the optical radiation and forms a mirror.

When the two end faces of the diode functioning as a reflector aredesigned as portions of two confocal cylindrical surfaces, the PNjunction plane extends perpendicularly to the axis of the cylinder.

The end face which is provided for the larger radius is preferablyimpermeable to optical radiation, while the end face provided for thesmaller radius is partially permeably mirrored for optical radiation.The focusing laser diode of the invention provides an intensive, smalllight source which is well suited for drawing photomasks onphotosensitive material. This permits the drawing of masks forsemiconductor integrated circuits on a relatively small scale. It mayalso be util ized to record sound traces and video images, and the like,on photosensitive recording media. Recording is effected, with adequatecooling and with the assistance of permanent light, for example, bylight pulses which are closely spaced adjacent each other.

In another embodiment of the laser diode of the invention, the end facehaving the smaller radius of curvature is impermeably mirrored foroptical radiation, while the end face having the larger radius ofcurvature is partially permeably mirrored for optical radiation. As aresult, a divergent bundle of rays is emitted from the laser diode viathe end face having the larger radius of curvature. The laser beam has alarge cross-sectional area. If necessary, the laser beam having a largecross-sectional area may be easily focused by means of auxiliary opticalcomponents such as, for example, lenses, either parallel or convergent,without damage to the lenses or their binding due to the laser beam. Thelenses or their binding may easily be damaged by bundles of intensivelaser rays hav ing small cross-sectional areas.

It is particularly expedient to provide better cooling for the laserdiode of the invention by providing both outer contact surfaces of thesemiconductor crystal, which surfaces extend in parallel with the PNjunction plane, with good heat conducting contact blocks. it is alsopreferable to provide the contact blocks with a cooling device. in orderto provide optimum cooling, it is particularly preferred to provideextensions for the semiconductor crystal extending perpendicularly tothe plane of the PN junction and having a length much greater than thewidest distance of the luminescence region, by a factor of l to 5, forexample.

ln order that the present invention may be readily carried into effect,it will now be described with reference to the accompanying drawing,wherein:

Fig. l is a perspective view of an embodiment of the laser diode oftheinvention;

FIG. 2 is a perspective view of another embodiment of the laser diode ofthe invention;

FIG. 3 is a perspective view of the laser diode of the present inventionwith cooling blocks affixed thereto; and

FIG. 4 is a schematic diagram of the laser diode of the invention withlighbresponsite sensors affixedthereto In the figures, the samecomponents are identified by the same reference numerals. FIG. 1illustrates a laser of my in vention for producing focused light. Thesemiconductor crystal 1 comprises a region of P conductivity type and aregion of N conductivity type having a contact area along which theplane ofa PN junction 2 extends. The end faces 3 and 4 of thesemiconductor crystal 1 function as a resonator for optical radiation.The end faces 3 and 4 are perpendicular to the plane of the PN junctionare designed, in the embodiment of FIG. 1 as portions of two confocalspherical surfaces. The PN junction 2 extends radially between the Nfaces 3 and 4 as shown in FIG. I.

The end face 3 of the semiconductor crystal I has a larger radius ofcurvature than the end face 4 thereof. The end face 3 is impermeable tooptical radiation and the end face 4 is mirrored and is partiallypermeable to radiation, so that the multi ple reflecting coherentoptical radiation is produced outside the laser diode via the partiallypermeable mirrored end face 4. The radiation which is produced outsidethe laser diode is concentrated at a focal point F. The distance ofthefocal point F from the end face 4 of the laser diode is determined bythe curvatu re of the two confocal spherical surfaces 3 and 4.

The semiconductor crystal 1 has a pair of sides, outer surfaces orcontact faces 5 and 6 extending in parallel with the plane ofthe PNjunction 2. The outer surfaces 5 and 6 are pro vided with electricalcontacts which are affixed thereto in electrical contact therewith, andthrough which the voltage is applied in the forward direction. Theelectrical contacts or electrodes, electrically contacting the sides 5and 6, are not shown in the H08. in order to enhance the clarity ofpresentation.

The embodiment of FIG. 2 of the laser diode of the inven' tion functionsto focus coherent light. The end faces 3 and 4 of the semiconductorcrystal 1 function has a reflector for the coherent optical radiationproduced therein at the plane ofthe PN junction 2. The end faces 3 and 4of the semiconductor crystal l are designed as portions of two confocalcylindrical surfaces. The plane of the PN junction 2 extendsperpendicularly to the axis of the cylinders and parallel to the twocontact faces 5 and 6 of the semiconductor crystal I. The light emittedfrom the partially permeably mirrored cylindrical surface portion 4 isfocused at a focal line F.

FIG. 3 shows a laser diode of the invention provided with two good heatconducting contact blocks 7 and 8. The contact block 7 is in contactwith and adjacent the contact face 5 of the semiconductor crystal 1 andthe contact block 8 is in contact with and adjacent the contact face 6of said semiconductor crystal. The contact faces 5 and 6 are parallel tothe plane of the PN junction 2, which PN junction extendsperpendicularly to the two confocal end faces 3 and 4 of thesemiconductor crystal 1. Better cooling may be provided by utilizing asuitable cooling device, which is not shown in the FIGS, with thecontact blocks 7 and 8.

FIG. 4 illustrates a focusing laser diode ofthe type of the inventionutilized for measuring surface roughness. To accomplish this, twoextending photosensitive structural components 9 and are utilized. Thephotosensitive structural component 9 extends from the contact face ofthe semiconductor crystal 1 perpendicularly to said contact face, andthe photosensitive structural component 10 extends from the contact face6 of said semiconductor crystal perpendicularly of said contact face. Asin the previously illustrated embodi ments of the laser diode: thecontact faces are parallel to the plane ofthe PN junction.

The focal point of the laser diode is utilized to scan a surface 0,either continuously or in pulse operation. When the surface 0 is planar,and the coherent light produced in the semiconductor crystal l impingesperpendicularly on the average, the light is reflected into the diodeand the scattered light is uniformly impinged upon the twophotosensitive elements or components 9 and 10. When the surface 0 isnonplanar, in the area of the light or focal point, the light isirregularly distributed and impinges upon the photosensitive components9 and 10. The inclination of the plane may be established from therelationship of the photocurrents produced by the photosensitivecomponents 9 and It). The ratio of the photocurrents provides the firstdifferential quotient of the configuration of the surface in a specificangular range. Electronic integrat on may be utilized to provide astandard for the elevations and depressions of the surface.

While the invention has been described by means ofspecific examples andin specific embodiments, 1 do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention 1 claim' I. A laserdiode for producing focused light, comprising a semiconductor crystalhaving a planar PN junction and two parallel end faces extendingperpendicular to the PN junction and conjointly forming a resonator foroptical radiation, said end faces comprising portions of two confocalsurfaces, said PNjunction extending between said two confocal surfacesin a radial plane relative to the focal locus, the one of said end facesat the greater radial distance from the focal locus being impermeable tooptical radiation and the other of said end faces being a mirrorpartially permeable to optical radiation.

2. A laser diode as claimed in claim 1, wherein each of said confocalsurface portions is of spherical configuration and the plane of said PNjunction extends through the center of the sphere.

3. A laser diode as claimed in claim I, wherein each of said confocalsurface portions is of cylindrical configuration and the plane of saidPN junction extends perpendicularly to the axis of the cylinder.

4. A laser diode as claimed in claim I, wherein said semiconductorcrystal has two contact faces on opposite sides of said crystalextending parallel to the plane of said PN junction, and furthercomprising electrical contact and heat sink structures in conductivecontact with the contact faces of said semiconductor crystal.

5. A laser diode as claimed in claim I, wherein said semiconductorcrystal has two contact faces on opposite sides of said crystalextending parallel to the plane of said PN junction, and furthercomprising a pair of electrical contact blocks of good heat conductingmaterial, each of said blocks being in conductive contact with acorresponding one of the contact faces of said semiconductor crystal.

6. A laser diode as claimed in claim 1, wherein said semiconductorcrystal has a dimension perpendicular to said PN junction which does notsubstantially exceed the luminescent region of said semiconductorcrystal.

7. A laser diode as claimed in claim 1, wherein said semiconductorcrystal has two contact faces on opposite sides of said crystalextending parallel to the plane of said PN junction, and furthercomprising a pair of light-responsive sensors, each of said sensorsbeing affixed to a corresponding one of said sides and extending awayfrom said semiconductor crystal substantially perpendicularly to thecorresponding side.

8. A laser diode as claimed in claim 7, wherein each of saidlight-responsive sensors is of area type and has a length which isgreater than the greatest distance between the contact faces of saidsemiconductor crystal.

1. A laser diode for producing focused light, comprising a semiconductorcrystal having a planar PN junction and two parallel end faces extendingperpendicular to the PN junction and conjointly forming a resonator foroptical radiation, said end faces comprising portions of two confocalsurfaces, said PN junction extending between said two confocal surfacesin a radial plane relative to the focal locus, the one of said end facesat the greater radial distance from the focal locus being impermeable tooptical radiation and the other of said end faces being a mirrorpartially permeable to optical radiation.
 2. A laser diode as claimed inclaim 1, wherein each of said confocal surface portions is of sphericalconfiguration and the plane of said PN junction extends through thecenter of the sphere.
 3. A laser diode as claimed in claim 1, whereineach of said confocal surface portions is of cylindrical configurationand the plane of said PN junction extends perpendicularly to the axis ofthe cylinder.
 4. A laser diode as claimed in claim 1, wherein saidsemiconductor crystal has two contact faces on opposite sides of saidcrystal extending parallel to the plane of said PN junction, aNd furthercomprising electrical contact and heat sink structures in conductivecontact with the contact faces of said semiconductor crystal.
 5. A laserdiode as claimed in claim 1, wherein said semiconductor crystal has twocontact faces on opposite sides of said crystal extending parallel tothe plane of said PN junction, and further comprising a pair ofelectrical contact blocks of good heat conducting material, each of saidblocks being in conductive contact with a corresponding one of thecontact faces of said semiconductor crystal.
 6. A laser diode as claimedin claim 1, wherein said semiconductor crystal has a dimensionperpendicular to said PN junction which does not substantially exceedthe luminescent region of said semiconductor crystal.
 7. A laser diodeas claimed in claim 1, wherein said semiconductor crystal has twocontact faces on opposite sides of said crystal extending parallel tothe plane of said PN junction, and further comprising a pair oflight-responsive sensors, each of said sensors being affixed to acorresponding one of said sides and extending away from saidsemiconductor crystal substantially perpendicularly to the correspondingside.
 8. A laser diode as claimed in claim 7, wherein each of saidlight-responsive sensors is of area type and has a length which isgreater than the greatest distance between the contact faces of saidsemiconductor crystal.